We keep finding water on Mars – here are all the places it might be

NASA's Mars Exploration Program includes two active rovers and three active orbiters. Concept studies have begun for a potential future Mars orbiter mission. — Martian water may be lurking beneath – or even above – the planet’s surface

NASA/JPL/USGS

Mars is not as arid as it may seem. Billions of years ago, the surface of the Red Planet rippled with oceans and rivers of liquid water, but now it seems that all of that fluid has disappeared, leaving behind a dusty wasteland. However, as we have explored the planet with orbiters, landers, rovers and even telescope images from afar, traces of water keep popping up.

Each hint tantalises researchers because of how crucial water is for living organisms and how helpful it could be for future exploration. Water has now been discovered all over Mars, in many different forms – here are five places it has been spotted.

1. Buried underground

The InSight Lander NASA ID: PIA22227 This artist's concept shows the InSight lander, its sensors, cameras and instruments. InSight is will take the first-ever-in-depth look at Mars' "inner space." InSight stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. Its three instruments are a seismometer, a heat flow probe, and a radio science experiment. These instruments will shed light on how warm and geologically active Mars still is, study its reflexes as it whips about in its orbit around the sun, and provide essential clues on the evolution of the rocky planets of our solar system. So while InSight is a Mars mission, it's also more than a Mars mission. InSight will launch between May 5 through June 8, 2018 from Vandenberg Air Force Base in California. https://photojournal.jpl.nasa.gov/catalog/PIA22227 — The InSight lander, visualised here, recently found another potential water reservoir on Mars

NASA/JPL-Caltech

Just beneath Mars’s parched surface lies a wonderland of water ice. These deposits are kept insulated by the layers of dust on top of them, but erosion and meteorite impacts can expose them to the prying eyes of our orbiters. A single ice deposit recently identified using data from the Mars Express orbiter seems to contain enough water to cover the entire surface of Mars in an ocean 1.5 to 2.7 metres deep.

It’s not just ice buried under the shifting orange sands. Hints of a huge lake beneath the planet’s south pole have been controversial – it may simply be wet silt or volcanic rock. But a new study using data from the InSight lander has revealed another possible reservoir of water near the planet’s equator. InSight found this water buried 11.5 to 20 kilometres underground by feeling for marsquakes and measuring how fast those seismic waves travelled, which revealed that the rocks those quakes were propagating through seemed to be saturated with water.

2. Frosting over the poles

Most surface ice on Mars is temporary. The polar layered deposits are thick stacks of permanent water ice at each pole, and the South Polar residual cap may be a permanent (although dynamic) layer of carbon dioxide ice as seen by NASA's Mars Reconnaissanc — Frost in a crater on Mars’s Northern Plains

NASA/JPL-Caltech/Univ. of Arizona

Getting at the buried water on Mars would be difficult, so perhaps a more promising reservoir for future explorers is bared right on the surface. The poles on Mars have ice caps just like on Earth, and we have known about them for decades. Many craters on Mars also have smaller ice sheets inside them. These are the only places on Mars’s surface that stay cold enough for ice to stick around.

However, there is also some transient frost that forms at high latitudes on Mars, where the air tends to be colder and more humid. On some frigid Martian mornings, volcanic peaks frost over as well, which is probably due to water vapour freezing out of the atmosphere.

3. Floating in the atmosphere

Mars Daily Global Image from April 1999 Twelve orbits a day provide NASA Mars Global Surveyor MOC wide angle cameras a global napshot of weather patterns across the planet. Here, bluish-white water ice clouds hang above the Tharsis volcanoes. — Mars’s atmosphere may hold hints of travelling water

NASA/JPL/MSSS

Because of the bitter cold and tenuous atmosphere on Mars, any liquid water on the surface would sublimate away, turning directly into gas and floating up into the air. Water vapour in the atmosphere is a sign of water and ice migrating across the planet’s surface to form frost, but it is only present in minuscule amounts. Occasionally, there is enough water vapour in one area to generate a few wispy clouds, but for the most part it is nearly negligible.

4. Running downhill

Recurring Lineae on Slopes at Hale Crater, Mars NASA ID: PIA19916 Dark, narrow streaks on Martian slopes such as these at Hale Crater are inferred to be formed by seasonal flow of water on contemporary Mars. The streaks are roughly the length of a football field. The imaging and topographical information in this processed, false-color view come from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. These dark features on the slopes are called "recurring slope lineae" or RSL. Planetary scientists using observations with the Compact Reconnaissance Imaging Spectrometer on the same orbiter detected hydrated salts on these slopes at Hale Crater, corroborating the hypothesis that the streaks are formed by briny liquid water. The image was produced by first creating a 3-D computer model (a digital terrain map) of the area based on stereo information from two HiRISE observations, and then draping a ...more Date Created:2015-09-28 — Dark, narrow streaks on Martian slopes like these at Hale Crater may be formed by seasonal water flow

NASA/JPL-Caltech/Univ. of Arizona

Perhaps the most controversial of the possible signs of water on Mars are recurring slope lineae, which are dark streaks that sporadically appear running down the sloped edges of craters. They were first discovered in 2011, and since then there has been lively debate among researchers about what causes them. They occur primarily in the warmest parts of the year, so they could be caused by ice melting and then running downhill before evaporating away – which would make them the only liquid water ever spotted on the surface of Mars. Or, they could be simple sand flows. Over time, the latter hypothesis has gained support, but some researchers hold out hope that there could be a trickle of liquid water on the Red Planet.

5. Trapped in rocks

This image from NASA's Mars Reconnaissance Orbiter shows one of millions of small (10s of meters in diameter) craters and their ejecta material that dot the Elysium Planitia region of Mars. The small craters were likely formed when high-speed blocks of rock were thrown out by a much larger impact (about 10-kilometers in diameter) and fell back to the ground. — The Red Planet’s rocks may have sucked up its water

NASA/JPL-Caltech/Univ. of Arizona

If Mars used to be covered in water, and now all that’s left is a bit of ice and a whole lot of dust and stone, where did all that water go? One possible solution is that it got slurped up into the rocks themselves. Mars rovers have found no shortage of minerals with water molecules incorporated into their chemical structures all over the planet.

This process is irreversible, so there is no way for us to get all that water back – but accounting for where all the water went is crucial to understanding what Mars was like before it dried out. That may be our best chance for understanding if Mars ever really was hospitable to life.

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